BRUSSELS, March 23 (Reuters) - NATO's top military commander
said on Sunday that Russia had built up a large force on
Ukraine's eastern border and he was worried Moscow may be eyeing
Moldova's mainly Russian-speaking separatist Transdniestria
region after annexing Crimea.

NATO's Supreme Allied Commander Europe, U.S. Air Force
General Philip Breedlove, voiced concern about Moscow using a
tactic of snap military exercises to prepare its forces for
possible rapid incursions into a neighbouring state, as it had
done in the case of Ukraine's Crimea region.

Russia launched a new military exercise, involving 8,500
artillery men, near Ukraine's border 10 days ago.

Breedlove said the Russian tactic should lead the 28-nation
Western military alliance to rethink the positioning and
readiness of its forces in eastern Europe so that they were
ready to counter Moscow's moves.

"A snap exercise puts an incredible force at a border. The
force that is at the Ukrainian border now to the east is very,
very sizeable and very, very ready," he said, speaking at an
event held by the German Marshall Fund, a thinktank.

"You cannot defend against that if you are not there to
defend against it. So I think we need to think about our allies,
the positioning of our forces in the alliance and the readiness
of those forces ... such that we can be there to defend against
it if required, especially in the Baltics and other places."

Ukraine is not a NATO member, but Moscow's intervention in
Crimea has caused alarm particularly in ex-Soviet republics in
the Baltics, which are now members of NATO.

NATO had tried to make Russia a partner but "now it is very
clear that Russia is acting much more like an adversary than a
partner," Breedlove said.

He voiced concern that Russia could have Transdniestria in
its sights after Crimea, saying that, in Russia's view, the
separatist region of Moldova was the "next place where
Russian-speaking people may need to be incorporated."

LINK-UP FEARS

Some of the elements of the Crimea scenario are also present
in Transdniestria, which lies on Ukraine's western border but is
just a few hundred kilometres (miles) from Crimea.

"There is absolutely sufficient (Russian) force postured on
the eastern border of Ukraine to run to Transdniestria if the
decision was made to do that and that is very worrisome,"
Breedlove said.

In Moscow, Deputy Defence Minister Anatoly Antonov said
Russia was complying with international troop limits near the
border with Ukraine, and international inspectors had conducted
missions in the last month to check on Russian troop movements.

"We have nothing to hide there," Antonov was quoted by the
state RIA and Itar-Tass news agencies as saying.

The Russian-speakers of Transdniestria seceded from Moldova
in 1990, a year before the dissolution of the Soviet Union, amid
fears that Moldova would shortly merge with neighbouring
Romania, whose language and culture it broadly shares.

The separatist region fought a brief war with Moldova in
1992 and it declared itself an independent state, but it remains
unrecognized by any country, including Russia.

The speaker of Transdniestria's separatist parliament urged
Russia last week to incorporate the region. In response, the
president of ex-Soviet Moldova warned Russia against considering
any move to annex Transdniestria.

Ukraine's Foreign Minister Andrii Deshchytsia told the
Brussels conference on Friday that Transdniestria should be a
big concern for Europe as well as Ukraine and Moldova because of
the risk Moscow could seek to link up pro-Russian regions in
Ukraine, Moldova and Georgia.

If Russia decided to connect Transdniestria with the Crimea
and Georgia's Abkhazia region, it would make a corridor that
would create a "very destabilising zone in Europe", he said.

FROZEN CONFLICTS

Breedlove said Russia appeared to be using these so-called
"frozen conflicts" in neighbouring countries as a tool to stop
them joining the European Union and NATO.

"If Russia is worried about a country moving towards the
West, the way to solve that is an incursion, a frozen conflict,
and now no one wants to think about bringing that nation aboard
into NATO because it might mean conflict with Russia," he said.

U.S. officials have said the Pentagon will more than double
the number of U.S. fighter jets on a NATO air patrol mission in
the Baltics and do more training with Poland's air force as it
strives to reassure allies alarmed by the crisis in Ukraine.

Breedlove said the United States was considering other steps
but declined to give details.

He said Russia's incursion into Crimea had run "very much
like clockwork" in contrast to its 2008 intervention in Georgia,
which suffered from a lot of military failings.

Russia started by cutting Ukrainian forces in Crimea from
their commanders using cable cuts, jamming and cyber attacks and
then surrounded them, he said.

Breedlove said Russia tried to create doubts over the
identity of gunmen in Crimea as part of a disinformation
campaign. Moscow officially denied deploying extra troops and
Russian soldiers in the region wore unmarked uniforms.

When military bases in Crimea were taken over, it was "a
thin veneer of locals in the front and a lot of men in green
(Russian troops) right behind," he said.
(Reporting by Adrian Croft; Editing by Rosalind Russell)